The field of the invention is the field of measuring the magnetization of the surface of an object by illuminating a broad area of the surface of the object with polarized light, and simultaneously imaging the surface at very high resolution with light scattered from the surface.
Lasers have been be used as illumination sources for. Laser beams are typically single mode beams or multimode beams, and the beam homogeneity and coherence properties of such beams may not be sufficient for application like high resolution imaging of magnetic materials, where most of the light incident on the material is thrown away in polarization detection schemes. U.S. application Ser. No. 09/386,017, filed on Aug. 30, 1999 by the present authors, discloses in great detail apparatus and methods for homogenizing laser beams for microscopic and other applications.
An excellent overview of microscope illuminators is included in S. Inoue, Video Microscopy, Plenum Press, New York, N.Y., 1986.
Experimental images of surface magnetization abound in the literature (see, for example, Hubert, A. and Schaefer, R., 1998, Magnetic Domains, Springer, Berlin (Chapter 2)), as they describe in-plane or out-of-plane M-components, but rarely both. M-sensitive images have been obtained using light optics, electron optics, and scanning probe methods. Although limited in spatial resolution to order 100 nm, the magneto-optic Kerr-effect microscope is the most convenient and efficient method to obtain images. Advantages include little or no sample preparation requirements, capability to view through an overcoat film, response out to Larmour frequencies, and efficiency of data collection. Kerr microscopes are of two types. One method utilizing light focused on the sample, renders images with spot photodetection and mechanical rastering (see, for example, Re, M. and Kryder, M. J., 1984, J. Appl. Phys., vol.55,2245; Kasiraj, P., Horn, D. E. and Best, J. S., 1987, IEEE Trans. Magn. vol. MAG-23, 2161; Heyes, N. A. E., Wright, C. D. and Clegg, W. W., 1991, xe2x80x9cObservation of magneto-optic phase contrast using a scanning laser microscopexe2x80x9d, J. Apl. Phys., col 68, 5322-5324). Another uses wide-field illumination, video detection and image processing. (see, for example, Frosch, A. and Schneider, J., 1980, IBM Tech. Discl. Bulletin, vol. 22,3260; Argyle, B. E. and Suits, F., 1985, xe2x80x9cLaser magneto-optic microscope for studying domain motions in thin film heads (Invited)xe2x80x9d, Digest of 1985 INTERMAG Conf.; Schmidt, W., Rave, W. and Hubert, A. 1985, xe2x80x9cEnhancement of magneto-optic domain observation by digital image processingxe2x80x9d, IEEE Trans. vol. MAG-21, 1596-1598). The prior art wide-field method of microscopy is illustrated schematically in FIG. 1, using large Hg-arc source 10. An offset aperture stop 12 produces oblique illumination 14. The inset 16 shows how, in a polarizing microscope, reducing aperture size confines illumination to a narrow region centered on one arm of the cross of extinction. The full aperture for conventional microscopy is stopped down for Kerr microscopy, as indicated in the inset.
It is an object of the invention to provide a method of measuring the magnetization of a material by illuminating the material with a light source of very carefully controlled uniformity, direction, and polarization, and imaging the material in a non-scanning system at very high resolution using light scattered from and within the surface of the material, and combining two or more high resolution images of the material to produce a high resolution image of a component of the magnetization of the material.
It is an object of the invention to produce high resolution images of at least two magnetic components of a material, wherein the relative positions of the material and the optical systems remain unchanged and wherein the magnetic field in the object remains unchanged.
The surface of the object is uniformly illuminated with a beam of substantially parallel polarized light incident on the surface at an angle 0 to the normal to the surface wherein the plane of incidence is in the polarization cross. Light scattered from the surface and from below the surface of the object which leaves in a substantially parallel beam substantially in the plane of incidence but with an angle 0 on the opposite side of the normal to the incident beam and which has polarization slightly different from the incident light is used to produce a first image the surface. Then, the illumination beam direction and the observation beam direction are exchanged, and a second image is produced. Subtraction of one image from the other produces a high resolution image of an in-plane component of the magnetization of the surface. This procedure may be repeated for a plane of incidence at 90xc2x0 to the first, and the second in-plane component of the magnetization of the surface may be obtained. The polar component of the magnetization may be obtained by rotating the plane of polarization of the combining two images taken by rotating polarization of the incident light slightly.